Fluid dynamic bearing devices are bearing units in which a shaft to be supported is supported with a lubricating film of fluid created in bearing clearances, so as to be capable of relative rotation. These fluid dynamic bearing devices have such characteristics as high-speed rotation, high rotation accuracy, and low noise. Making the best use of those characteristics, they have been widely used in recent years as bearings intended for spindle motors to be mounted on information devices, including magnetic disk drives such as HDD and FDD, optical disc drives such as CD-ROM, CD-R/RW, and DVD-ROM/RAM, and magneto-optical disk drives such as MO, and fan motors to be mounted on personal computers (PC) and the like for the sake of cooling heat sources.
For example, a fluid dynamic bearing device built in a HDD spindle motor has a radial bearing portion for supporting a shaft member in radial directions and a thrust bearing portion for supporting it in thrust directions. The radial bearing portion is often configured as a dynamic bearing which has a dynamic pressure generating portion for generating the dynamic pressure effect of a lubricating fluid in the radial bearing clearance. When the radial bearing portion is configured as a dynamic bearing, dynamic pressure generating grooves are formed in either one of the inner periphery of the bearing sleeve and the outer periphery of the shaft member as the dynamic pressure generating portion (for example, see patent document 1).
The bearing sleeve mentioned above is typically fixed to a predetermined position inside a housing. Concerning this bearing sleeve to be fixed to a housing, a bearing sleeve has been known, for example, which has dynamic pressure generating portions formed at two axially separated positions on its inner periphery (see the foregoing patent document 1). For the purpose of increasing the bearing span between the radial bearing portions further, it has also been known that two bearing sleeves having dynamic pressure generating portions are axially arranged in a row (for example, see patent document 2), and that a spacer (also referred to as a filler piece) is interposed between two bearing sleeves (for example, see patent document 3).    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-232353    Patent document 2: Japanese Patent Application Laid-Open No. Hei 11-269475    Patent document 3: Japanese Patent Application Laid-Open No. Hei 11-155254